Fluid pressure responsive firing device



y 1963 w. R. BROCKWAY ETAL 3,095,815

FLUID PRESSURE RESPONSIVE FIRING DEVICE Filed Oct. 21, 1960 2 Sheets-Sheet 1 FIG. F|G.2

INVENTORS WILLIAM R. BROCKWAY FRANK A. LOVING GEORGE A. NODDIN ATTORNEY y 2, 1963 w. R. BROCKWAY ETAL 3,095,815

FLUID PRESSURE RESPONSIVE FIRING DEVICE Filed Oct. 21, 1960 2 Sheets-Sheet 2 INVENTORS WILLIAM R. BROCKWAY FRANK A. LOVING GEORGE A. NODDIN ATTORNEY United States Patent FLUID PRESSURE RESPONSIVE FIRING DEVICE William R. Brockway, Thorofare, Frank A. Loving,

Wenonah, and George A. Noddin, Sewell, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Get. 21, 1960, Ser. No. 64,087 3 Claims. (Cl. 102-70) The present invention relates to initiators and more particularly to pressure-responsive initiators.

For activities in which the detonation of explosive charges below the surface of a body of water is desired, such as for seismic exploration, underwater signalling, echo-ranging for detection purposes, and destruction of undersea craft, the need exists for a reliable and accurate initiator, responsive to the hydrostatic pressure of the water at some predetermined depth. The availability of such initiator obviates the need for wires leading from the surface to the charge or for timing devices to cause actuation of an initiator.

A number of mechanical pressure-responsive devices for actuating a firing pin are known; these devices possess the disadvantages of being relatively bulky, expensive, and subject to mechanicalfailure. Propagation detonators actuated by the collapse of the shell are commercially available; these devices function reliably only when subjected to a pressure surge such as from the detonation of a nearby explosive charge and are not reliable in shallow depths.

Accordingly, an object of this invention is to provide an economical, reliable and accurate pressure-responsive initiator.

The foregoing object is achieved in accordance with this invention by providing a pressure-responsive initiator comprising a tubular shell integrally closed at one end, and arranged in succession from said closed end a base detonating charge, a priming charge, an anvil, and a percussion-sensitive ignition charge, said anvil having an aperture leading from said ignition charge to the priming charge; a transversely movable piston sealing the open end of the shell, a flexible striker arm fastened to the inner end of the piston, the striker arm preferably being curved so that the free end is pointed toward the side wall of the shell, and an arresting element aligned with the free end of the striker arm between the free end and the ignition charge, whereby the free end is prevented from contacting the ignition charge until the inward movement of the piston as the result of increased external pressure is sufli-- cient to bend the striker arm to a degree that the free end slips off the arresting element and snaps onto the ignition charge.

Preferred embodiments of the present invention are illustrated in the accompanying drawings. In the drawings, FIGURE 1 represents a sectional view of an embodiment of the present invention, FIGURE 2 represents a sectional view of an alternative embodiment and FIG- URE 3 represents a sectional view of the embodiment of FIGURE 1 when subjected to hydrostatic pressure.

Referring now to the figures in greater detail, in FIG- URE l, 1 represents a metal shell integrally closed at one end, 2 is a base charge of a detonating explosive, 3 is a priming explosive charge, and 4 is an anvil locked in the shell by peripheral crimp 5. A portion of priming charge 3 is contained within the transverse aperture 6 of anvil 4, and positioned on top of anvil 4 adjacent to aperture 6 is igniting charge 7 of a percussion-sensitive explosive. integrally formed at one edge of anvil 4 is a striker arm arrester 12 for striker arm 11 attached to piston 8 located at the open end of shell 1. A pair of rings 9 seal the piston and pin 10 locks it in place.

In FIGURE 2, the components are as in FIGURE 1 except that coil spring 13 has been added, providing a 3,095,815 Patented July 2, 1963 device more suitable for higher pressures. In FIGURE 3, all components are as described for FIGURE 1, except that the effect of hydrostatic pressure is indicated.

The operation of the assembly of this invention is as follows. When the unit is to be used, locking pin 10 is removed to release piston 8. When the unit is then submerged, increasing hydrostatic pressure encountered with increasing depth forces piston 8 inwardly of shell 1 against the pressure of the air entrapped within the shell, and, in the case of the embodiment shown in FIGURE 2, against the resistance of coil spring 13. As the inward movement continues, the end of striker arm 11 comes into contact with arrester 12. When the striker arm has moved inwardly sufiiciently for the end to clear arrester 12, the end snaps onto the igniting charge 7, which, being percussion-sensitive, becomes ignited and in turn initiates priming charge 3 which then sets off base charge 2.

The pressure at which the striker arm is released from the arrester is dependent upon a number of factors, such as the weight of the piston, the length of the air chamber between the piston and the anvil, the frictional resistance of the piston to inward movement, the stiffness of the striker arm, and, when an additional spring is present, the strength of this spring. Thus, by proper selection of the appropriate factors, a pressure-responsive initiator can be produced to be actuated upon arrival at any preselected depth.

The striker arm used in the proposed device is attached at one end to the piston, the free end is pointed towards the side wall of the shell and is aligned with the arresting element. Since the striker arm does not rest on the arresting element, there is no tension exerted on the arm when there is no hydrostatic pressure on the detonator. This absence of tension not only makes the detonator very reliable because the striker arm does not change in its resistance to bending, but also places the detonator in a safe condition for handling. The fact that the striker arm rests on the arresting element when pressure is exerted until the critical point is reached allows a quick release of striking energy to set off the percussion-sensitive pellet reliably.

The following examples serve to illustrate specific embodiments of the present invention. All pressures were measured on a 2-pound increment pressure gauge.

Example I Twenty-five detonators similar to that shown in FIG- URE 1 were prepared, and fired by submerging them in water which was under nitrogen pressure. The detonator was constructed as follows: The tubular container consisted of a gilding metal shell having an inner diameter of 0.5 inch and a length of 2.4 inches; the anvil was cold rolled steel; the piston was cold rolled steel with a length of 0.375 inch; the safety pin consisted of a length of 0.059 inch diameter steel wire. The striker arm was 0.029 inch diameter spring steel a length of 0.687 inch, flat on top with a 0.156 inch radius curve, followed by a straight length of a 0.125 inch radius curve and terminating in a straight length 0.125 inch long, the tip of which is aligned 0.062 inch above the arresting element. The percussion-sensitive mixture used was an adhesive-backed toy cap.

The percussion-sensitive composition fired in all 25 cases. The range of pressures at which detonation occurred as from 74-94 p.s.i.ga. and the average pressure was 81.4 p.s.i.ga.

Example II Ten detonators were prepared and fired as in Example I except that the anvil was 0.062 inch higher than the above. A mixture of 75% lead salt of dinitro orthocresol, 20% potassium chlorate, and 5% selenium was placed in the hole of the anvil, an additional ignition mix of boron/red lead was added below the anvil and a 0.375 inch long lead carrier was added containing 11.5 grains per foot lead azide in the center as a base charge. The range of pressure at which firing occurred was from 58-70 p.s.i.ga. and the average was 64 p.s.i.ga.

As can be seen from the examples, the proposed detonator fires very reliably. The shots in the first series of tests fired within a range of 20 p.s.i.ga. and in the sec 0nd, of 12 p.s.i.ga. The pressure-sensitive detonators of the prior art fire within a range of 50 p.s.i.ga.

The anvil and arresting device may be of any design, straight or irregular, wherein the arresting device holds the striker arm until critical pressure is reached and wherein the striker arm can snap off the arresting device down onto the percussion-sensitive mixture. The arresting device may be annular or occupy only a portion of the inner periphery of the shell.

In the latter embodiment, the striker arm is kept in alignment with the arresting device by the locking pin until the device is ready to be used. The normal friction of the sealing rings is sufiicient to prevent rotation when pressure is applied.

The striker arm is preferably made of a spring steel, although it may be of a material of sufficient resiliency to snap onto the percussion-sensitive material after it is moved past its contact with the arrester.

The materials of the shell, anvil or compression spring are not critical and any conventional ignition, base, or percussion-sensitive composition can be used in the device.

Although the present invention has been described in detail in the foregoing, it will be apparent to those skilled in the art that many variations are possible without departure from the scope of the invention. We intend, therefore, to be limited only by the following claims.

1. A pressure responsive initiator for detonation of explosive charges at a predetermined depth below the surface of a body of water which consists essentially of a tubular shell integrally closed at one extremity, a piston slidably mounted within and closing the other extremity of said shell, a base charge of detonating explosive and a priming charge of explosive sequentially positioned from said integrally closed extremity, an anvil positioned contiguous to said priming charge, said anvil comprising a diaphragm secured in peripheral engagement with the inner wall of said shell and a striker arm arrester extending from said diaphragm toward said piston, said diaphragm being provided with an aperture therethrough adjacent said striker arm arrester, an ignition charge filling said aperture, a percussion sensitive explosive cap secured on said diaphragm adjacent said aperture and in propagating relationship to said ignition charge, a striker arm secured to said piston and extending to engage said arrester, said arm being adapted to disengage said arrester and strike said percussion cap upon exertion of a predetermined pressure by said piston, and removable means for locking said piston in position.

2. The initiator of claim 1 wherein a spring means is interposed between said piston and said anvil.

3. The initiator of claim 1 wherein said striker arm is a flexible striker arm of resilient material.

References Cited in the file of this patent UNITED STATES PATENTS 694,265 Von Gortz Feb. 2, 1902 1,514,743 Taylor Nov. 11, 1924 2,398,718 Rasmussen Apr. 16, 1946 2,547,820 Hammer Apr. 3, 1951 2,763,212 McCaslin Sept. 18, 1956 2,848,949 Diels Aug. 26, 1958 2,850,979 Hardwick Sept. 9, 1958 FOREIGN PATENTS 126,326 Great Britain May 15, 1919 

1. A PRESSURE RESPONSIVE INITIATOR FOR DETONATION OF EXPLOSIVE CHARGES AT A PREDETERMINED DEPTH BELOW THE SURFACE OF A BODY OF WATER WHICH CONSISTS ESSENTIALLY OF A TUBULAR SHELL INTEGRALLY CLOSED AT ONE EXTREMITY, A PISTON SLIDABLY MOUNTED WITHIN AND CLOSING THE OTHER EXTREMITY OF SAID SHELL, A BASE CHARGE OF DETONATING EXPLOSIVE AND A PRIMING CHARGE OF EXPLOSIVE SEQUENTIALLY POSITIONED FROM SAID INTEGRALLY CLOSED EXTREMITY, AN ANVIL POSITIONED CONTIGUOUS TO SAID PRIMING CHARGE, SAID ANVIL COMPRISING A DIAPHRAGM SECURED IN PERIPHERAL ENGAGEMENT WITH THE INNER WALL OF SAID SHELL AND A STRIKER ARM ARRESTER EXTENDING FROM SAID DIAPHRAGM TOWARD SAID PISTON, SAID DIAPHRAGM BEING PROVIDED WITH AN APERTURE THERETHROUGH ADJACENT SAID STRIKER ARM ARRESTER, AN IGNITION CHARGE FILLING SAID APERTURE, A PERCUSSION SENSITIVE EXPLOSIVE CAP SECURED ON SAID DIAPHRAGM ADJACENT SAID APERTURE AND IN PROPAGATING RELATIONSHIP TO SAID IGNITION CHARGE, A STRIKER ARM SECURED TO SAID PISTON AND EXTENDING TO ENGAGE SAID ARRESTER, SAID ARM BEING ADAPTED TO DISENGAGE SAID ARRESTER AND STRIKE SAID PERCUSSION CAP UPON EXERTION OF A PREDETERMINED PRESSURE BY SAID PISTON, AND REMOVABLE MEANS FOR LOCKING SAID PISTON IN POSITION. 